Depends. You should have around the same stand over height on the new 17.5 650b but the wheelbase should be shorter snd will have a slightly longer top tube. Ride it see how it feels. But is prolly go with a 17.5

I ride a 17" in ALL wheel sizes. The size of the wheel does not change what size frame I ride. If you went down to a 26" bike would that mean you would need to size up 2 sizes to 19"? Trying to follow the logic here.